Electrical musical instrument



Dec. 10, 1940. L. HAMMOND ELECTRICAL MUSICAL INSTRUMENT Filed Dec. 8, 1938 ,zaum i Patented Dec. 10, 1940 UNITED STATES PATENT OFFICE 18 Claims.

My invention relates generally to electrical musical instruments, and more particularly to improvements in the control systems for such instruments, whereby improved musical results may be obtained. The invention is an improvement upon the electric organ disclosed in my prior Patent No. 1,956,350, granted April 24, 1934, and has for its primary object to improve the attack and decay characteristics of the tones produced by the instrument.

A further object is to provide an electrical musical instrument in which some of the tones have a substantially rectangular intensity envelope while others have envelopes in which the intensity of the tone increases gradually upon depression of the key, and upon release of the key decays gradually.

A further object is to provide an improved means for keying the tone signals in an electrical musical instrument.

Other objects will appear from the following description, reference being had to the accompanying drawing which is a schematic wiring diagram showing representative portions of a complete instrument.

As more fully disclosed in my aforesaid patent, the electric organ to which the invention relates comprises a plurality of electromagnetic generators, one for each frequency required in the production of the notes of the musical scale, whether as a fundamental or a harmonic frequency. Each of the generators comprises a tone wheel of which six are shown in the drawing, these tone wheels bearing the reference characters W22, W34, W4I, W46, W50 and W53, the

numerical portion of the reference character indicating the note number, Co being considered as note No. 1. These tone wheels are rotated through a suitable gearing by a synchronous or other constant speed motor, means being provided to assure rotation of the tone wheels at a very accurately maintained constant speed, such v means including resilient and frictional driving elements for damping hunting.

Each of the tone wheels is cut to have a plurality of high points equally spaced along its periphery, and these high points pass closely ad'- jacent the wedge-shaped end of permanent magnets IM to vary the reluctance of the magnetic field thereof at a rate corresponding to the frequency of the signal to be generated. Each of the permanent magnets I M is provided with a coil I02 which is connected through a condenser C1 to an auto transformer I04. The other terminal of the coil I02 is connected to a common return conductor I06 which is likewise connected to the other terminal of the effective primary of the auto transformer I04.

The effective secondary of the auto transformer I04 is connected to a conductor I08 from which the signals are transmitted, through resistors IIO, each of approximately 15 ohms resistance. As more fully described in my aforesaid patent, these resistors supply the signals generated by the tone wheels to switches II2 operated by keys of the manuals and pedals, 'of which the keys A1, A2, E3, A3, C4# and E4 are illustrated. The switches II2 are adapted to make contact with bus bars II4 of which there is one for each of the partials. Thus, for example, the third bus bar II 4 may serve as a collector for the fundamental frequencies. while the fourth to ninth bus bars II4 serve as collectors for the second, third, fourth, fifth, sixth and eighth harmonics respectively. There will ordinarily be a set of bus bars II4 for each manual, and a similar set of collector conductors will be provided for the pedal clavier. The first and second bus bars II4 may be utilized as collectors for the sub-fundamental frequency (i. e. a frequency one-half that of the. fundamental), and for the fifth of the fundamental (i. e. the third harmonic of the subfundamental-frequency 1.5 times that of the fundamental) The signals controlled by the keys A1, A2, etc.,

, are supplied to pre-selected taps on the primary II6 of an output transformer II 8 through circuits controlled by preset keys of which two, keys PKI and PK2, are illustrated. These keys operate switches I20 which are adapted to make contact with the bus bar II4 respectively, and are selectively connected to conductors I22.

The conductors I22 are connected to various taps of the primary I I6 of the output transformer, the taps being arranged so that successive taps will represent apparently equal increases in intensity of the sound.

The secondary I24 of the output transformer II8 has one terminal grounded and the other connected through suitable filter circuits I26, a tremulant control I28, and a. volume control I30 to a preamplifier I32. The preamplifier supplies the signal to a power amplifier which is connected to power amplifier I34, which is connected to a speaker I36.

The circuits thus far described are, with minor exceptions, identical to those disclosed in' my aforesaid patent. In the present instrument, however, additional circuits are provided for transmitting signals from the generators to the I40 of the triodes.

,nected through a resistor R1 ment, although if desired, similar notes of the manuals and the pedal clavier may each be provided by a single additional circuit. These additional signal transmission circuits each comprises a triode. of which six are illustrated in the drawing, being designated T22, T34, T4I, T46, T50 and T53, to indicate the note numbers of the circuits with which they are associated. While these triodes are indicated as being separate tubes, it will be understood that in actual practice, twin triode tubes may be used, or special tubes incorporating three or more triodes in a single tube envelope may be employed.

The grid I of each of the tubes T22, T34, etc., is connected to a bus B22, B34, etc. Resistors I42 are connected between the conductorsl08 and the buses. These resistors are of relatively high value, ranging from .25 to 4 megohms, and may thus be arranged to supply a mixture of harmonically related frequencies to each of the grids For example, the grid I40 of the tube T22 may have its bus B22 connected to the conductors I08 associated with the generators for notes 22, 34, M, 40, 50, 53 and 58, and thus be supplied with signals of the frequencies of the fundamental and the second, third, fourth, fifth, sixth and eighth harmonics. Resistors I.42 by which such connection is made are of selected values, so that the voltages derived from these generators bear the value relationships necessary to produce the desired tone quality.

The value of the resistors I42 is so high with respect to the values of the resistors I I0 that they will not. appreciably affect the amplitude of the signals supplied through the latter resistors. Similarly, the values of the resistors I42 are so high with respect to the impedance of the generators that even though a plurality of resistors I42 are connected in parallel between a. single grid I40 and the common return conductor I06, there will be no appreciable robbing.

The cathodes I44 of the triodes are connected to ground through a common conductor I40.

The conductor I05, connected to one of the terminals of each of the tone wheel generators, is biased negatively with respect to ground by a battery I48 so as to provide the necessary grid bias upon the triodes.

The plate potential for the triodes is provided by a suitable potential source .8 which is connected, through a tapped primary I50 of a transformer I52 and a conductor I54, to key switch contacts I50. The contacts I55 have associated therewith a switch I58 which may be similar .to the switches H2 and operated by the keys A1, A2, etc., in a similar manner. The switch I50 is conto the plate I00 of the associated triode, the plate being likewise connected to the common conductor I54 throu h a condenser C2. The resistor R1 may have a value in the order of 3000 ohms..

The secondary I02 of the transformer I52 has one terminal grounded, and the other terminal connected to the liveinput line of the tremolo control device I30. In this way, any signals transmitted through thetriodes are combined with the signals transmitted through the resisters Ill and coalesce therewith.

me instrument is played in the of an organ. Upon depression of one of the keys, for example, A1, circuits from the plurality of harmonically related generators are completed through the resistances III and switches H2, and

usual manner through the conductor preset I switches I20 and I22 to the tapped primary hence through the The relative intensities of the partials are controlled by the adjustment of the connections between the preset key switches I20 and the conductors I22, so that a signal in which the partials are of the desired relative amplitude is produced in the secondary I24 of the output transformer I I8. This signal is suitably filtered through filter circuits (which may be of a type more fully disclosed in my aforesaid patent), and have their over-allintensity modulated at will by a tremulant device I20. Asuitable swell pedal provided for the operation of the volume control may be. adjusted to provide the desired intensity of the signal supplied to the preamplifier, and thus control the loudness of the sound produced by the speaker I30.

In addition to the above results, depression of any one of the keys, A1, etc., closes its associated switch I55, I58 and thus connects the B supply to the plate I00 of the associated triode. This connection is, however, through the resistor R1, which is of sufllciently high value (approximately 0.5 megohm) with respect to the capacitance of the condenser C2, so that the potential on the plate I00 does not rise instantaneously to the potential of the B supply, but instead, rises graduallyto this value. As a result, the plate current through the tube, as controlled by the voltage signal on'the grid I40 thereof, builds up gradually to its maximum value. Similarly, upon releasing the, key and opening the switch I55, I50, the potential on the plate will not immediately drop to zero, but due to the condenser C2, will drop gradually to a value at which the tube is cut off.

This gradual increase in the plate current, and the subsequent gradual decrease of the plate current, causes a signal having a gradual attack and gradual decay to be produced in the secondary of I the transformer I52.

Furthermore, as the potential of the plate approaches cut-off potential, the alternating current signal in distorted more and more, thus causing increasing harmonic distortion of the signal as a lesser and lesser portion of the signal wave is transmitted through the tube. This latter effect is desirable musically since it induces new frequencies which are exact harmonics of the frequencies in the input, and which therefore differ from the frequencies ofthe tempered musical scale.

If desired, the grid bias may be made adjustable so that the signal will be distorted throughout theperiod that the key remains. depressed. By, properly regulating the grid bias, the distortionmay be made to take place mainly with respect to the lower frequencies-"and the frequencies of highest amplitude.

Since the frequencies supplied by the generators are not, in all instances, exact harmonics of one another, but instead, are as close to the exact harmonics-as is permitted due to the tempering of the musical scale, the distortion of a given frequency supplied to one of the triodes will the plate circuit will gradually be i The relative intensities of the signals supplied to the volume control device by the transformers H8 and I52 may readily be controlled by connecting the conductor I54 to a selected one of the taps of the primary I of the transformer I52. In this way, the degree of eifectiveness of the gradual attack of the signals provided by the triodes may be easily adjusted, it being understood that when the conductor I54 is connected to the plus terminal of the current supply B, no portion of the signals supplied by the triodes will be transmitted to the amplifier, and the instrumentmay then be played to produce tones of the character produced by the electric organ shown in my aforesaid Patent No. 1,956,350.

In the complete instrument, it may be desirable to provide several buses, such as the bus B21, for each of the triodes together with suitable switching means, whereby any one of the buses may be selectively connected to the grid I40 of the triode. In this way, each bus could be connected to its associatedgenerators through resistors I42 of different pre-selected values, so that the quality of the tone signal'transmitted through the triode could be readily selected.

It is interesting to note that if the attack is not made too rapid (i. e., if the value of the resistor R1 is not too small with respect to the value of the condenser C2) there will be no appreciable transients set up upon closing and opening the switch I56, I58, because the current which starts flowing at the instant the key is depressed, flows through a local circuit including the resistor R1 and condenser C2, and does not flow through the primary I50 of the transformer I52. Thus, the possibility of key clicks is eliminated.

While I have shown a particular embodiment of my invention, it will be apparent to those skilled in the art that numerous modifications and variations thereof may be made without departing from the underlying principles of the invention. Furthermore, while particular values of various circuit elements are specified, it will be apparent that these values are merely illustrative and that they may in general be changed throughout a wide range, especially if compensatory changes are made in other portions of the circuit. I therefore desire, by the following claims,'to include within the scope of my invention, all such modified and similar equivalent constructions whereby substantially the results of my invention may be obtained by substantially the same means.

I claim:

1. In an electrical musical instrument, the combination of a plurality of generators of the frequencies of the notes of the tempered musical scale, an output circuit having means for ampli-- fying and translating electrical impulses into sound, key operated signal control means comprising an electron discharge device having a cathode, grid, and plate, and having its plate current controlled by the key, and a plurality of high resistance elements connecting the grid of said device to a plurality of said generators.

2. The combination set forth in claim 1 in which said signal control means includes a cohdenser and resistance network in the plate circuit of said device.

3. The combination set forth in claim 1 in which said generators are of relatively low impedance, and in which the impedances of said re- 'sistance elements are many times as great as the impedance Mom of said generators.

4. The combination set forth in claim 1 in which there is a source of plate current, a condenser connected between said source and said plate, a resistor having one terminal connected to said plate, and a circuit including said key operated switch connecting said source to the other terminal of said resistor.

5. In an electrical musical instrument, the combination of a plurality of generators of electrical impulses corresponding in frequency to the notes of the tempered musical scale, an output circuit including means for amplifying and translating said impulses into sound, a key, a plurality of circuits controlled-by said key for supplying impulses from said generators to said output circuit, and additional switch controlled by said key, an electron discharge device having a cathode, grid and plate, resistors of relatively high value connecting a plurality of said generators to, said grid, a source of platecurrent, a transformer having a primary and a secondary and having one terminal of its primary connected to said source, a conductor connecting the other terminal of said primary with said additional switch, a resistor connected between said additional switch and said plate, a condenser connected between said conductor and said plate, and means for connecting the secondary of said transformer to said output circuit.

6. In an electrical musical instrument, the combination of a generator of electrical impulses of a musical frequency, an output circuit including an amplifier and electroacoustic translating means, an electron discharge device having a cathode, grid and plate, a high resistance element connecting said generator to said grid, a source of a plate current, a resistor, a manually operable switch for connecting said source to said'plate through said resistor, and a condenser permanently connecting said plate to said source, the relative values of said resistor and condenser being such that upon closure of said switch, the plate potential will increase at a perceptibly gradual rate, and upon opening said switch, the potential on said plate will decrease at a perceptibly gradual rate.

7. In an electrical musical instrument, the combination of a plurality of low impedance generators of electrical impulses of harmonically related frequencies, an output circuit including electroacoustic translating means, a manually output circuit, and means including one of said switches for conditioning said device for operation.

8. The combination set forth in claim 7 in which the means for conditioning said device for operation includes means for causing the device to commence operating gradually.

9. The combination set forth in claim 7 in which the means for conditioning said device for operation includes means for causing the device to commence operation with gradually increasing effectiveness upon depression of said key. and upon release of said key to continue operation with gradually decreasing efl'ective 4 ness, thereby to obtain gradual attack and decay in the tone produced.

10. The combination set forth in claim. 7 in which the means for conditioningvsaid device for operation includes a condenser and resistance network in circuit with one of said switches.

11. The combination set forth in claim 'I in which said device has a cathode, grid and plate, and a source of plate current, and in which said means for conditioning said device for operation includes a condenser and a resistor arranged to be connected in parallel between said plate and said source upon closure of one of said switches.

12. The combination set forth in claim 7 in which said device has a cathode, grid and plate and in which a biasing potential source is connected in said input circuit of said device.

13. In an electrical musical instrument, the combination of a ,low impedance generator of electrical impulses, an output circuit including electroacoustic translating means, a manually operable key, a switch operated by said key, an electron discharge device having input and output circuits, a connection between said generator and the input circuit of said device, said connection having an impedance at least ten times greater than that of said generator, means for connecting the output of said device to said output circuit, and means including said switch for conditioning said device 'for operation.

14. The combination set forth in claim 13 in which the means for conditioning saiddevice for operation includes means for causing the device to commence operating gradually.

15. The combination setforth in claim 13 in 5 which the means for conditioning said device for operation includes means for causing the device to commence operation with gradually increasing eiiectiveness upon depression of said kelnand upon release of said key to continue operation with gradually decreasing eflectiveness, thereby to obtain the desired gradualattack and decay in the tone produced.

16. The combination set forth in claim 13 in which the means for conditioning said device 15 for operation includes a condenser and resistance network in circuit with said switch.

1'7. The combination set forth in claim 13 in 1 which said device has a cathode, grid and plate; and a source of plate current, and in which 20 saidmeans forconditioning said device for operation' includes a condenser and a resistor connected in parallel between said plate and said source upon closure of said switch.

18. The combination setforth in claim 13 in 25 which said device has a cathode, grid and plate and in which a biasing potential source is con-, nected in said input circuit of said device.

LAURENS HAMIMOND. 

